Technical Field
The instant disclosure relates to a direct current to direct current (DC-DC) converter, and in particular relates to a synchronous buck DC-DC converter and method thereof.
Related Art
For power management applications, synchronous buck direct current to direct current (DC-DC) converters have various control modes. When using a constant on-time control mode, DC-DC converters can operate directly with output voltage ripples, requiring no special pulse width modulation (PWM) signal generator circuit or loop compensation network. This control scheme can greatly simplify the topologies of power supply systems which adapt DC-DC converters and improve transient responses of power supply systems with a wide range of load and output capacitance, as well as enhance reliability of power supply systems.
In a typical topology of a conventional constant on-time control mode synchronous buck DC-DC converter, the output voltage, usually used as a threshold voltage, is compared with the voltage across the capacitor in a timer to generate a timing signal. And the timing signal and a control voltage signal are used to control the “ON” time of the power transistor, thereby to regulate the output voltage.
For existing constant on-time control mode schemes, on-resistance of a power transistor may result in that a switching period of the power transistor varies with load current, which affects the operation and performance of DC-DC converters and also limits the applications of DC-DC converters.